User manual

16 – Effective Motor Current Change for Neutrally
Bouyant MMP (in mA)
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Item 16 = Item 15 / 2.
17 – Ballast Air Weight Correction based on 4 g/mA
Effective Motor Current (in g)
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Item 16 × (4 g / mA)
18 – Ballast Water Weight Correction based on
density of lead (in g)
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Item 17 × (.907)
19 – Corrected Ballast Weight (in g)
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Item 14 + Item 18
Determining Air and Water Weights
The operator should not be required to make the air and water weight measurements,
however, a complete description is included here to provide an understanding of the process, the
accuracy requirements, and the known pitfalls of making these measurements. Remember that
McLane provides a re-ballast service upon request.
IMPORTANT
The air weight should be measured on a scale with an accuracy of ± 10 gram (10g).
Accuracy of the water weight measurement may be affected by microscopic bubbles on
the exposed surfaces of the MMP. A continuous sheet of bubbles can coat the MMP within a few
minutes of immersion. The bubbles add a significant amount of buoyancy to the profiler and
invalidate the weight measurement. To prevent bubble formation, submerge the MMP to a depth
of two meters or more.
In addition, the density of the MMP has a distinct temperature dependence. Changes
occur in the MMP water weight during temperature equilibration. A plot of these changes over a
five hour period is shown in Figure 5-1. In this case the water temperature was approximately
18°C and the initial temperature of the MMP was approximately 25°C. The ultimate change in
weight was approximately 40 g (out of a total mass of ~70000 g) or 6 g/°C.
5-6